The specific aim of the proposed research is to demonstrate proof-of- concept for a new whole-body indirect calorimeter for the measurement of energy expenditure in infants. The measurement of energy expenditure in infants is important for a number of reasons, including determination of energy requirements in health and disease, the metabolic cost of growth, optimal environmental conditions, and response to different feeds. Due to the current difficulty in obtaining energy expenditure measurements in this population, values are commonly estimated from tables or regression equations. These estimates show considerable variability and are of limited value in metabolic studies. The proposed instrument will incorporate new technologies related to the key measurements required for indirect calorimetry: gas analysis and airflow control. Furthermore, the overall system design will lead to enhanced accuracy and stability of measurement. Should this development prove successful, the result will be a new indirect calorimeter for infants that meets the following criteria: (1) non-invasive, (2) accurate, (3) stable, (4) maintains normal environment (21% O2, 0.03% CO2), (5) easy to use, and (6) portable. The availability of such a product could significantly contribute to the study and care of infants under a variety of circumstances. PROPOSED COMMERCIAL APPLICATION: There are commercial applications in research and health care for the resultant whole-body indirect calorimeter; including the study of energy balance, growth, and enhanced nutritional requirements under certain conditions, e.g., in burn patients. The component technologies used in the system, specifically the methods of airflow measurement and oxygen analysis, are also commercially marketable technologies having both health care and industrial applications.